PHASE I: Investigation of the compressive strength and void ratio of the specimens obtained from the two plants.
Picture showing two different aggregate types from sources.
The distance between these two plants is approximately 100 miles away. Initial visual examination was to look at the color of two aggregate sources. Plant A’s aggregates appeared to be darker than that of Plant B. The properties of two aggregate sources were tested and the results were depicted in Table 1.
Properties of aggregate sources from two plants
Virgin Aggregate Specific Gravity and Water Absorption Properties without Admixtures |
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|
Plant A |
Plant B |
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Property |
Coarse |
Fine |
Combined |
Coarse |
Fine |
Combined |
Bulk (Dry) Sp. Gravity |
2.768 |
2.697 |
2.728 |
2.770 |
2.702 |
2.731 |
SSD Sp. Gravity |
2.777 |
2.722 |
2.746 |
2.816 |
2.761 |
2.785 |
Apparent Sp. Gravity |
2.794 |
2.766 |
2.778 |
2.903 |
2.871 |
2.886 |
Water Absorption (%) |
0.34 |
0.93 |
0.53 |
1.66 |
2.19 |
1.95 |
LA Abrasion @ 100 Rve. (virgin aggregate) |
4 |
4 |
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LA Abrasion @ 500 Rve. (Virgin aggregate) |
23 |
18 |
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·Four Mix design formulas were used to prepare the specimens using two types of aggregates.
·Compressive strength and void ratio tests were performed.
Compression test results of pervious concrete specimens
Gradation mix design |
Compression (psi) at 7 days Group A |
Compression (psi) at 7 days Group B |
Compression (psi) at 28 days Group A |
Compression (psi) at 28 days Group B |
1/2"+ #4 with fiber |
1920 |
3340 |
N/A |
N/A |
1/2"+ #4 with fiber |
1200 |
2780 |
N/A |
N/A |
1/2"+ #4 |
1130 |
2630 |
1560 |
2650 |
1/2"+ #4 |
1378 |
2715 |
1770 |
2890 |
3/8"+ #4 |
1420 |
2500 |
1440 |
2803 |
3/8"+ #4 |
1290 |
3200 |
1360 |
2706 |
#4 |
1170 |
2100 |
1390 |
2560 |
#4 |
1260 |
2250 |
1885 |
3070 |
PHASE II: Evaluating the use of fiber in the mixtures
Two different types of fibers were used in the pervious concrete mixtures (Febermesh @ 150 and Febermesh @ 500).
Specification of fiber
Fiber Name |
Specific gravity |
Fiber Length (in) |
Application Rate |
Febermesh@150 |
0.91 |
Graded |
1.0-1.5 lbs/cu yard
|
Febermesh@500 |
0.91 |
0.25-2 |
0.1% by volume |
The compressive strength tests and void ratio tests were used to investigate the effectiveness of the two types of fiber using different application rates. All specimens were made from the same mix design formula using 3/8” + #4 aggregate with the addition of varying fiber types and fiber contents.
Compressive strength and void ratio test results
Fiber (Types and application rate) |
Compression (psi) at 7 days
|
Compression (psi) at 28 days
|
Void ratio |
Fiber 150, 0.9 kg/m3 |
N/A |
4875 |
N/A |
Fiber 150, 0.6 kg/m3 |
2860 |
7035 |
22% |
Fiber 500, 1.2 kg/m3 |
2245 |
N/A |
17% |
Fiber 500, 0.9 kg/m3 |
2895 |
6330 |
19% |
Note: The results of the control specimen (without fiber) were 2,800 psi (28 days) and the void ratio was tested at 18%
Failure comparison of two specimens
(Failure of a specimen with fiber on the left and Failure of a specimen without fiber on the right)
A. 
B. 
By adding the fiber to the mixture of the pervious concrete, the failure mode under compressive test has been changed. As shown in the Fig. A, the stress within the pervious concrete cylinder has been partially absorbed by the fibers as compared with the one without fiber (Fig. B) where the failure envelope crosses the entire specimen.
PHASE III: Investigation of the freeze-thaw resistance (on-going)
The objective of this phase is investigation of the freeze-thaw resistance. Because of the delay in the delivery of the Gilson HM-120 Automatic Freeze-Thaw Apparatus, the team has just begun the freeze-thaw cycle test in November 2013.
HM-120 Automatic Freeze-Thaw Apparatus
Freeze-thaw cycle diagram after completion of 32 cycles
•Freeze-Thaw cycle durability test of the pervious concrete has been running in the Construction Materials lab at NAU. The test specimens are made of ½”+ #4 aggregate and 3/8”+ #4 aggregate with different types of fiber according to the ASTM C 666/C 666M - 03
•The weight and length changes of tested specimens will be measured at different cycles in order to evaluate the durability of the specimens.
Pictures of the freeze-thaw-cycle apparatus with specimens undergoing test.
Results of freeze-thaw test at 32 cycles
Sample number |
Dry weight (g) |
Void Ratio |
Initial SSD Weight (g) |
Initial Length Comparmeter Reading (mm) |
32 cycles SSD Weight (g) |
32 cycles Length Comparmeter Reading (mm) |
17.a |
6834.00 |
0.24 |
6885.70 |
1.65 |
6909.00 |
2.56 |
17.b |
5848.00 |
0.21 |
5890.58 |
2.34 |
5910.00 |
2.77 |
19.a |
6274.00 |
0.25 |
6335.06 |
2.42 |
6349.00 |
1.16 |
19.b |
5886.00 |
0.26 |
5952.21 |
2.45 |
5970.00 |
2.11 |
20.a |
5751.00 |
0.28 |
5825.02 |
3.03 |
5834.00 |
1.56 |
20.b |
5924.00 |
0.24 |
5998.02 |
2.86 |
6006.00 |
1.06 |
21.a |
5993.00 |
0.22 |
6056.30 |
3.09 |
6061.00 |
1.04 |
21.b |
5989.00 |
0.23 |
6068.46 |
2.08 |
6053.00 |
0.68 |
22.a |
6258.00 |
0.19 |
6333.55 |
2.57 |
6332.00 |
0.71 |
22.b |
6532.00 |
0.18 |
6606.48 |
2.52 |
6620.00 |
0.57 |
As shown in the above table, the weight and length of the specimens did not change significantly after 32 cycles. The readings were slightly increased due to the fact the moisture stays in specimens.